There are many olefin polymers which can be made into fibers and filaments. This includes polyethylene, polypropylene, polybutene, polypentene, and ethylene and propylene copolymerized with other olefinic monomers such as higher olefins and conjugated dienes. Olefin polymers are known for their hydrophobic properties. Therefore, wettability of such polymers, including those in fibrous or filament form, is achieved by means of wetting agents provided in, or on, the polymer fibers or filaments.
Such fibers or filaments are useful in producing battery separators (e.g., U.S. Pat. No. 3,847,676); disposable diapers (e.g. U.S. Pat. No. 4,073,852); wiper materials (e.g., U.S. 4,307,143); papers (e.g. U.S. Pat. No. 4,273,892); and filter aids (e.g., U.S. Pat. No. 4,274,971).
U.S. Pat. No. 4,189,420 discloses, inter alia, certain ethylene polymers blended with a polybutene and a mixed glyceride having at least one acyl group of 2 to 6 carbon atoms and at least one acyl group containing 8 to 22 carbon atoms.
U.S. Pat. No. 3,048,266 discloses, inter alia, a polyolefin film containing an anti-fog agent of polyethylene oxide derivative.
U.S. Pat. No. 3,048,263 discloses, inter alia, a polyolefin film containing an anti-fog agent comprising a monoglyceride of a fatty acid and optionally a diglyceride of a fatty acid. An example of a monoglyceride disclosed therein is glyceryl monostearate.
U.S. Pat. No. 2,462,331 discloses, inter alia, the incorporation into polyethylene of polyhydric alcohol esters of metal salts of either saturated or unsaturated monocarboxylic fatty acids.
U.S. Pat. No. 4,578,414 discloses an olefin polymer, preferably a linear low density polyethylene copolymer (LLDPE), having compounded therewith a wetting agent, which is used in forming wettable fibers and/or filaments. The wetting agent has at least one of the following: (1) an alkoxylated alkyl phenol along with a mixed mono-, di- and/or tri-glyceride, or (2) a polyoxyalkylene fatty acid ester, or (3) a combination of (2) and any part of (1).
Whereas it is known that virtually any thermoplastic polymer can be extruded as a coarse strand or monofilament, many of these, such as polyethylene and some ethylene copolymers, have not generally been found to be suitable for the making of fine denier fibers or multi-filaments. A fine denier fiber or filament refers to an extruded strand of denier less than about 15. It is also recognized that the mechanical and thermal conditions experienced by a bundle of filaments, whether in spinning staple fibers or in multi-filaments yarns, are very different to those in spinning monofilaments. The fact that a given man-made polymer can be extruded as a monofilament, does not necessarily herald its use in fine denier or multi-filament extrudates.
The synthetic fibers are produced as continuous filaments by a process known as melt spinning. The plastic pellets are fed in to a hopper and melted in a single screw extruder. The molten polymer is filtered and then metered before being forced through a spinnerette that contains thousands of small holes. The fibers are then solidified by using air and as the fibers are drawn by the action of rollers by sequentially increasing their speeds. The drawn filaments are then wound onto the spools. The spools are made into bunches called tows and cut into staple fibers according to the manufacturer's requirements.
The fibers are the main constituents of fabrics and nonwovens. Nonwovens are unconventional textile assemblies that are obtained by processes other than weaving or knitting. In recent years, there has been a phenomenal growth in the usage of nonwovens in personal hygiene, diapers, adult incontinence, medical, construction, geotextiles and automotive applications. Nonwovens can be made from both natural and synthetic fibers and a combination of both. Usually, the fibers are obtained or extruded and bonded into thin sheets by heat or mechanical or chemical means. The main types of nonwovens used in the market include the spunbonded and melt blown types. The details of these types of materials and their manufacturer will be explained in the following paragraphs. Very often, more than one type of nonwoven is used to make laminates or composite structures. The nonwovens are sometimes further bonded to provide them with adequate strength for other operations.
In the manufacture of a spunbond nonwoven, polymer chips are typically fed through a hopper and melted in the single screw extruder. Some machines also have side feeder capability to feed additives, such as pigments. The molten polymer is metered and then forced through several thousand spinnerett holes to form fine continuous filaments. The filaments are drawn and entangled through the action of a venturi and deposited on a collection belt. The unbonded, entangled fibers are then passed through two heated calendar rolls for thermal bonding of the fibers to each other at points of contact. The nonwoven fabric is then wound and shipped to converting applications where the fabric is made into final products. Alternatively or in addition, the fibers are also bonded through needle-punching and chemical bonding. The polymers typically used in spunbonding are polyolefins, such as polyethylene and polypropylene, polyamides and polyesters. Polypropylene is most commonly used with a melt flow rate in the range between 30-40. Polypropylene is easy to process and cost-effective when compared to other polymers. The spunbond polypropylene nonwovens are used in baby diapers, napkins, feminine hygiene products, laminates, adult incontinence, medical garments, agricultural covers, etc.
In the manufacture of a melt blown nonwoven, polymer chips are fed through a hopper and melted in the single screw extruder. Some machines have additional side feeding capacity for additives, including pigments or color masterbatches. The molten polymer is forced through very fine die holes that are situated either vertically or horizontally. The fibers are then subjected to the action of very hot air at very high velocities to elongate the fibers resulting in fibers with sub-micron diameters. The fibers are bonded to each other at contact points as they cool down. Usually, there is no separate bonding process. The melt blown products are typically used in filters, wipes, battery separators, and insulators.